Image rotation in image forming apparatus based on determination of power consumption by heater elements

ABSTRACT

An image forming apparatus includes an image forming device, a heater, and a control circuit. The control circuit is configured to generate first energization data based on at least part of first raster image data representing a first image to be formed on a first page, and then compress the first raster image data into first compressed image data. The control circuit is also configured to generate second energization data based on at least part of second raster image data representing a second image to be formed on a second page, and then compress the second raster image data into second compressed image data. The control circuit is configured to further determine whether rotation of the second image by a predetermined degree will lower power consumption based on a comparison of the first energization data to the second energization data.

FIELD

Embodiments described herein relate generally to an image formingapparatus and an image forming method.

BACKGROUND

In the related art, there is an image forming apparatus including afixing device that includes a plurality of heater elements arrangedalong a main scanning direction. In such an image forming apparatus,printing is performed by independently energizing the heater elements toselectively heat predetermined heating regions corresponding todifferent an image sub-portions. In such a fixing device, sinceenergization of the plurality of heater elements can be controlledindependently, it is not necessary to supply power to the heaterelements that do not need to be energized if, for example, the sheetbeing printed does not overlap particular heating elements. For thatreason, power consumption can be reduced. In some fixing devices, theamount of power expected to be consumed for printing print data at oneorientation can be compared to the amount of power expected to beconsumed for printing the print data a different orientation and theprinting of the print data can be performed at the orientation havingthe lower power consumption.

However, in general, the image forming apparatus in the related art mustat least temporarily compresses the print data and store the compressedprint data in a storage device for various analyses of expected powerconsumption. Therefore, when actually printing, it may take additionaltime to print because the image forming apparatus calculates expectedpower consumption only after decompressing the print data beforeprinting, then determines whether image rotation is desirable, and thenperforms the image rotation processing.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of an overall configurationof an image forming apparatus according to an embodiment.

FIG. 2 is a block diagram illustrating a hardware configuration of animage forming apparatus according to an embodiment.

FIG. 3 is a diagram illustrating heating regions for a plurality ofheater elements included in a heating unit.

FIG. 4 is a flowchart of energization data generation processing.

FIG. 5 is a diagram illustrating a method of generating energizationdata.

FIG. 6 is a diagram illustrating an example of energization datagenerated based on print data illustrated in FIG. 5.

FIG. 7 is a diagram illustrating processing when there are print datafor multiple pages.

FIG. 8 is a diagram illustrating an example of energization data of theprint data in the example of FIG. 7.

FIG. 9 is a diagram illustrating an example of energization data of theprint data in the example of FIG. 7 after image rotation.

FIG. 10 is a timing chart illustrating temporal transitions oftemperature of a fixing device and supplied power when an imagecorresponding to second print data is rotated by 0°.

FIG. 11 is a diagram illustrating a temporal transition of thetemperature of the fixing device and the supplied power when an imagecorresponding to second print data is rotated by 180°.

FIG. 12 is a diagram illustrating a result of a logical operation whenan image corresponding to the second print data is rotated by 0°.

FIG. 13 is a diagram illustrating a result of the logical operation whenan image corresponding to the second print data is rotated by 180°.

FIG. 14 is a flowchart illustrating a flow of processing when printingprint data.

DETAILED DESCRIPTION

An image forming apparatus according to an embodiment includes an imageforming device, a heater, and a control circuit. The image formingdevice configured to form images (e.g., toner images) on sheets. Theheater includes a plurality of heater elements arranged in a firstdirection corresponding, for example, to the sheet-width direction. Theheater is configured to fix images to the sheets conveyed from the imageforming device. The control circuit is configured to generate firstenergization data indicating energization states of each of the heaterelements based on first raster image data representing a first image tobe formed by the image forming device, then compress the first rasterimage data into first compressed image data, and store the generatedfirst energization data and the first compressed image data in astorage. The control circuit is also configured to generate secondenergization data indicating energization states of each of the heaterelements based on second raster image data representing a second imageto be formed by the image forming device after the first image, thencompress the second raster image data into second compressed image data,and store the generated second energization data and the secondcompressed image data in the storage. The control circuit determineswhether rotation of the second image by a predetermined degree willlower power consumption in the printing of the first and second images.The determination is based on a comparison of the first energizationdata to the second energization data.

FIG. 1 is a diagram illustrating an example of the overall configurationof an image forming apparatus 1 according to an embodiment. The imageforming apparatus 1 according to the embodiment is a multi-functionperipheral (MFP). The image forming apparatus 1 executes printing by animage forming processing and an image fixing processing. The imageforming processing forms an image (e.g., a toner image) on a sheet. Theimage fixing processing fixes the image on the sheet. The sheet is, forexample, paper on which text, characters, or images can be formed. Ingeneral, the sheet may be any material as long as the image formingapparatus 1 can form an image thereon.

The image forming apparatus 1 includes an image reading unit 10, acontrol panel 20, an image forming unit 30, a sheet storage unit 40, afixing device 50, conveyance rollers 61 a and 61 b, paper dischargerollers 62 a and 62 b, and a control device 70.

The image reading unit 10 reads an image on a document according toreflected light contrast or the like. For example, the image readingunit 10 reads an image from a reading target sheet set on a documentreading platen and generates image data. The image reading unit 10records (stores) the generated image data. The recorded image data maybe transmitted to an information processing apparatus via a network. Therecorded image data may be processed for forming a corresponding imageon the sheet by the image forming unit 30 as print data.

The control panel 20 includes a display unit and an operation unit. Thedisplay unit is a display device such as a liquid crystal display and anorganic electro luminescence (EL) display. The display unit displaysvarious information related to the image forming apparatus 1 inaccordance with the control of the control device 70. The operation unitincludes a plurality of buttons or the like. The operation unit receivesa user input operation. For example, the operation unit receives a printexecution instruction. The operation unit outputs a signal correspondingto the input operation performed by the user to the control device 70.The display unit and the operation unit may be configured as anintegrated touch panel.

The image forming unit 30 executes image forming processing.Specifically, the image forming unit 30 forms an image on the sheetbased on the image data generated by the image reading unit 10 or imagedata received via a communication path. For example, the image formingunit 30 forms a toner image on the sheet with toner.

The image forming unit 30 includes a transfer belt 31, an exposure unit32, developing devices s 33Y, 33M, 33C, and 33K, photoconductive drums34Y, 34M, 34C, and 34K, and a transfer unit 35.

The transfer belt 31 is an endless intermediate transfer member. Thetransfer belt 31 rotates in the direction indicated by the arrow(counterclockwise in the figure) by rotation of the roller(s).

The exposure unit 32 is provided at a position facing thephotoconductive drums 34Y, 34M, 34C, and 34K between the developingdevices 33Y, 33M, 33C, and 33K and a respective charger (not separatelyillustrated). The exposure unit 32 irradiates the surface(photoconductive layer) of each of the photosensitive drums 34Y, 34M,34C, and 34K with laser light based on the image data. The directionalong which a photoconductive drum is scanned with the laser light iscalled the main scanning direction, and the direction orthogonal to themain scanning direction is called the sub-scanning direction. Forexample, in the present embodiment, the main scanning directioncoincides with the axial direction of the photoconductive drum, and thesub-scanning direction coincides with the rotation direction of thetransfer belt.

Charges stored on the surface (photoconductive layer) of each of thephotoconductive drums 34Y, 34M, 34C, and 34K disappear due to theirradiation of the laser light. As a result, an electrostatic pattern isformed on the surface of each of the photoconductive drums 34Y, 34M,34C, and 34K at the positions irradiated with the laser light. In otherwords, electrostatic latent images are formed on the surfaces of thephotoconductive drums 34Y, 34M, 34C, and 34K by irradiation of the laserlight from the exposure unit 32. The exposure unit 32 may use lightemitting diode (LED) light instead of laser light in some examples. Theexposure unit 32 is controlled to emit light based on the image dataunder the control of the control device 70.

The developing devices 33Y, 33M, 33C, and 33K supply toners to thephotoconductive drums 34Y, 34M, 34C, and 34K. For example, thedeveloping device 33Y develops the electrostatic latent image on thesurface of the photoconductive drum 34Y with a yellow (Y) toner. Thedeveloping device 33M develops the electrostatic latent image on thesurface of the photoconductive drum 34M with a magenta (M) toner. Thedeveloping device 33C develops the electrostatic latent image on thesurface of the photoconductive drum 34C with a cyan (C) toner. Thedeveloping device 33K develops the electrostatic latent image on thesurface of the photoconductive drum 34K with a black (K) toner.

The developing devices 33Y, 33M, 33C, and 33K form toner images asvisible images on the photoconductive drums 34Y, 34M, 34C, and 34K. Thetoner images formed on the photoconductive drums 34Y, 34M, 34C, and 34Kare transferred (primary transfer) onto the transfer belt 31 by aplurality of primary transfer rollers. The plurality of primary transferrollers are provided at positions facing the photoconductive drums 34Y,34M, 34C, and 34K with the transfer belt 31 interposed therebetween.

The transfer unit 35 includes a support roller 35 a and a secondarytransfer roller 35 b. The transfer unit 35 transfers the toner image onthe transfer belt 31 to a sheet 41 at a secondary transfer position U.The secondary transfer position U is a position where the support roller35 a and the secondary transfer roller 35 b face each other with thetransfer belt 31 interposed therebetween. The transfer unit 35 applies atransfer bias controlled by a transfer current to the transfer belt 31.The transfer unit 35 transfers the toner image on the transfer belt 31to the sheet 41 by the transfer bias. The transfer current is controlledby the control device 70.

The sheet storage unit 40 includes one or more paper feed cassettes. Thesheet feed cassette stores sheets 41 of a predetermined size and apredetermined type. The paper feed cassette includes a pickup roller.The pickup roller picks up the sheets 41 one by one from the paper feedcassette. The pickup roller supplies the picked-up sheet 41 to aconveyance unit 80.

The fixing device 50 executes image fixing processing. Specifically, thefixing device 50 fixes an image (for example, a toner image) formed onthe sheet 41 by heating and pressing the sheet 41. The fixing device 50according to the present embodiment includes a heating unit having aplurality of heat generating elements that are arranged in the mainscanning direction and can be controlled to be heated independently foreach predetermined heating region. Each of the heater elements generatesheat when energized. That is, the energized heater element generatesheat, and the non-energized heater element does not generate heat. Theheater element applies heat to the sheet 41. A press roller is installedat a position facing the heating unit. The press roller presses thesheet 41 against the heating unit.

The transport rollers 61 a and 61 b supply the sheet 41 fed from thepaper feed cassette to the image forming unit 30. The transport rollers61 a and 61 b are installed at opposing positions.

The paper discharge rollers 62 a and 62 b discharge the sheet 41 afterthe fixing device 50 to the discharge unit. The paper discharge rollers62 a and 62 b are installed at opposing positions.

The control device 70 controls each functional unit of the image formingapparatus 1.

The conveyance unit 80 conveys the sheet 41. The conveyance unit 80includes a conveyance path and a plurality of rollers. The conveyancepath is a path through the image forming apparatus 1 along which thesheet 41 is conveyed. The roller(s) move/convey the sheet 41 by rotatingaccording to the control of the control device 70.

FIG. 2 is a block diagram illustrating a hardware configuration of theimage forming apparatus 1 according to the embodiment. FIG. 2illustrates only a schematic hardware configuration of the image formingapparatus 1 in the present embodiment.

The image forming apparatus 1 includes an image reading unit 10, acontrol panel 20, an image forming unit 30, a sheet storage unit 40, afixing device 50, a control device 70, an auxiliary storage device 120,and a network interface 130. Each functional unit is connected via asystem bus 2 so that data communication is possible.

The fixing device 50 includes a fixing control circuit 51, a heatingunit 52, and a press roller (not separately illustrated).

The fixing control circuit 51 controls the heating of the heating unit52 in response to an instruction from the control device 70.Specifically, the fixing control circuit 51 supplies power to a heaterelement that is a target for heating (hereinafter, referred to as“target heater element”) in response to an instruction from the controldevice 70. On the other hand, the fixing control circuit 51 cuts offpower supply to heater elements other than the target heater elements(hereinafter, referred to as “non-target heater elements”). For example,a power supply source and heater elements may be connected to each othervia switches.

In this case, the fixing control circuit 51 turns on a switch connectedto a target heater element so as to electrically connect the powersupply source and the target heater element, thereby supplying power tothe target heater element. As a result, the target heater elementgenerates heat by, for example, resistive heating or the like. Inaddition, the fixing control circuit 51 turns off the switch connectedto the non-target heater element so as to make the power supply sourceand the non-target heater element non-conductive, thereby cutting offthe power supply to the non-target heater element. Thus, the non-targetheater element does not generate heat.

The heating unit 52 heats the sheet. The heating unit 52 includes aplurality of heater elements 53-1 to 53-N (N is an integer of 2 or more)(see FIG. 2) in the main scanning direction. The heater elements 53-1 to53-N are independently controlled by turning on or off a respectiveswitch connected thereto. For example, the heating unit 52 is a heatingsource including a plurality of heater elements 53-1 to 53-N. Differentidentification information is given to each of the heater elements 53-1to 53-N, and the heater elements 53-1 to 53-N can thus be individuallydistinguished. In the following description, the heater elements 53-1 to53-N are described as the heater elements 53 when not distinguished fromeach other.

FIG. 3 is a diagram illustrating a heating region of the plurality ofheater elements 53-1 to 53-N included in the heating unit 52 in thepresent embodiment. In the present embodiment, the case where theheating unit 52 includes six heater elements (53-1 to 53-6) will bedescribed as an example, but the number of heater elements 53 is notlimited thereto. Each of the heater elements 53-1 to 53-6 heats a rangecorresponding to one of the depicted regions A to F. For example, theheater element 53-1 heats the range indicated by the region A.Similarly, the heater element 53-2 heats the range indicated by theregion B. The heater element 53-3 heats the range indicated by theregion C. The heater element 53-4 heats the range indicated by theregion D. The heater element 53-5 heats the range indicated by theregion E. The heater element 53-6 heats the range indicated by theregion F.

The control device 70 includes a control unit 71, a read only memory(ROM) 72, a random access memory (RAM) 73, and an image processing unit74. The control device 70 or a part thereof may be referred to as acontrol circuit. The control unit 71 is, for example, a processor suchas a central processing unit (CPU) or a graphics processing unit (GPU).The control unit 71 controls the operation of each functional unit ofthe image forming apparatus 1. The control unit 71 executes variousprocessing by loading the program stored in the ROM 72 in the RAM 73 toexecute the program. An application specific integrated circuit (ASIC)may incorporated and used to provide certain functions realized by thecontrol unit 71. The ASIC is an example of a dedicated circuit forrealizing a specific function.

The ROM 72 stores a program for operating the control unit 71. The RAM73 is a memory that temporarily stores data used by each functional unitincluded in the image forming apparatus 1. For example, the RAM 73stores raster data obtained by converting print data, which istransmitted from an external device or generated by the image readingunit 10. The RAM 73 may store digital data generated by the imagereading unit 10. The RAM 73 may temporarily store jobs and job logs.

The image processing unit 74 uses the print data as input data toperform image processing on the input data. The image processing unit 74comprises an integrated circuit for image processing such as afield-programmable gate array (FPGA) or an application specificintegrated circuit (ASIC). The print data processed by the imageprocessing unit 74 is temporarily stored in the auxiliary storage device120, then converted into raster data by the control unit 71 and loadedon the RAM 73.

The image processing unit 74 reads the raster data loaded on the RAM 73and converts the raster data into encoded data (code data) for datastorage. That is, the image processing unit 74 compresses raster data.In addition, the image processing unit 74 scans the raster data anddetermines a region where there is an image to be printed. Here, thedetermination on the region where the image to be printed is present isperformed for each region obtained by dividing the print data intopredetermined sections. The image processing unit 74 determines thatthere is an image in a region where the number of pixels greater than acertain numerical value representing a color in raster data is equal toor greater than a threshold. On the other hand, the image processingunit 74 determines that there is no image in a region where the numberof pixels greater than a certain numerical value representing a color inraster data is less than the threshold. According to this processing,the image processing unit 74 can discriminate between noise and an image(or image portion).

The image processing unit 74 generates energization data of the frontportion and the rear portion of each heater element 53 in the sheetconveyance direction by using the determination result of each region.The front portion in the sheet conveyance direction represents a tipportion in the sheet conveyance direction when divided into thepredetermined sections. The rear portion in the sheet conveyancedirection represents a rear end portion in the sheet conveyancedirection when divided into the predetermined sections. The energizationdata is information on the necessity of energization of each heaterelement 53. For example, the energization data includes information onthe necessity of energization of the front portion and the rear portionof each heater element 53. For example, for each of the heater elements53-1 to 53-6, a value of “1” is displayed when energization is necessaryand “0” is displayed when no energization is necessary. The imageprocessing unit 74 stores the generated code data (also referred to asencoded data) and energization data in association with each other inthe auxiliary storage device 120. The image processing unit 74 may storethe code data and the energization data in the RAM 73 in associationwith each other. The image processing unit 74 executes generationprocessing for code data and energization data by the number of piecesof print data.

The image processing unit 74 reads the code data and the energizationdata stored in the auxiliary storage device 120 when printing isexecuted. When there are a plurality of pieces of data to be printed,the image processing unit 74 reads all code data and energization datacorresponding to all the data to be printed. In the followingdescription, a case where there are two pieces of data to be printedwill be described. Here, first print target data is defined as firstprint data, and second print target data is defined as second printdata. In this case, the image processing unit 74 reads the code data andenergization data corresponding to the first print data, and the codedata and energization data corresponding to the second print data fromthe auxiliary storage device 120. The image processing unit 74determines whether or not the code data corresponding to the secondprint data (hereinafter, referred to as “second code data”) needs to berotated based on the read energization data. When the image is rotated,the image processing unit 74 converts the second code data to third codedata, which represents a third image obtained by rotating the secondimage, and decompresses the third code data. For example, when the imagecorresponding to second code data is rotated, the image processing unit74 changes the arrangement of the second code data such that the imagewill be rotated by 180°.

On the other hand, when the image corresponding to the second code datais not rotated, so the image processing unit 74 does not change thearrangement of the second code data, (that is, there can be considered arotation of the image by) 0° and decompresses the second code data.

The auxiliary storage device 120 is, for example, a hard disk or a solidstate drive (SSD) and stores various data. The various data are, forexample, digital data, print jobs, job logs, encoded data, andenergization data.

The network interface 130 transmits and receives data to and from otherdevices. Here, the other device is an information processing device suchas a personal computer. The network interface 130 operates as an inputinterface and receives print data or instructions transmitted from otherdevices. An instruction transmitted from the other device includes aprint execution instruction. The network interface 130 operates as anoutput interface and transmits data to the other device.

FIG. 4 is a flowchart illustrating a flow of energization datageneration processing performed by the image forming apparatus 1 in thepresent embodiment. It is assumed that the print data is converted intoraster data and loaded on the RAM 73 at the start of the processing ofFIG. 4.

The image processing unit 74 reads raster data from the RAM 73 (ACT101). The image processing unit 74 converts the read raster data intocode data (ACT 102). The image processing unit 74 generates energizationdata based on the read raster data (ACT 103).

FIG. 5 is a diagram illustrating aspects of a method of generatingenergization data in the present embodiment. In FIG. 5, the labelledregions “A” to “F” along the main scanning direction represent heatingranges of the heater elements 53-1 to 53-6. Further, the labelledregions “1” to “8” along the sheet conveyance direction (that is, thesub-scanning direction) correspond to ranges of the raster data dividedat a predetermined interval along to the sheet conveyance direction. Inthis example, the range “1” is the front (leading) portion along thesheet conveyance direction, and the range of “8” is the rear (trailing)portion along the sheet conveyance direction. It is assumed in thisexample that there is an image 200 in the print data. Each depictedsection formed by the divisions into ranges of “A” to “F” and the rangesof “1” to is considered an image presence/absence determination region.

In the example of FIG. 5, there is an image along the sheet conveyancedirection from the front portion (range “1”) to the rear portion (range“8”) for each of the ranges of “A” and “B” along the main scanningdirection. Therefore, the heater element 53-1 corresponding to heatingthe “A” range and the heater element 53-2 corresponding to heating the“B” range are the target heater elements in this example. The imageprocessing unit 74 determines that energization is necessary in theranges of “A” and “B” from the front portion to the rear portion.Further, the image processing unit 74 determines that energization isnot necessary in any of the ranges of “C” to “F” along the entire length(front to rear) along the sheet conveyance direction. As a result, theimage processing unit 74 generates energization data like FIG. 6 basedon the print data illustrated in FIG. 5.

FIG. 6 is a diagram illustrating an example of the energization datagenerated based on the print data illustrated in FIG. 5. Theenergization data illustrated in FIG. 6 includes a value “1” in columnsfor “A” and “B” in both the row for the front portion and the row forthe rear portion. A value “0” in columns for “C” to “F” in both the rowfor the front portion and the row for the rear portion is in theillustrated energization data of FIG. 6.

Referring back to FIG. 4, the image processing unit 74 stores thegenerated code data and the energization data in association with eachother in the auxiliary storage device 120 (ACT 104). Thereafter, theimage processing unit 74 determines whether or not there is other printdata (ACT 105). If there is other print data (ACT 105: YES), the imageprocessing unit 74 reads the other print data and again executes theprocessing after ACT 101.

On the other hand, if there is no other print data (ACT 105: NO), theimage processing unit 74 ends the processing of FIG. 4.

FIG. 7 is a diagram illustrating processing in the present data whenthere are multiple pieces of print data. FIG. 7 illustrates an examplein which the first print data and the second print data are continuouslyprinted. In FIG. 7, the ranges “A” to “F” and the ranges “1” to “8” areagain as described in conjunction with FIG. 5. In FIG. 7, it is assumedthat there are an image 200 in the first print data and an image 201 inthe second print data.

In this example, in the first print data, the region from the frontportion to the rear portion in the ranges of “A” and “B” is a printtarget. That is, in the first print data, the heater element 53-1 thatheats the range “A” and the heater element 53-2 that heats the range “B”are the target heater elements. In the second print data, the regionfrom the front portion to the rear portion in the ranges of “E” and “F”is a print target. That is, in the second print data, the heater element53-5 that heats the range “E” and the heater element 53-6 that heats therange “F” are target heater elements. The image processing unit 74generates energization data for each of the first print data and thesecond print data based on the above results.

FIG. 8 is a diagram illustrating an example of energization data of eachprint data item depicted in the example of FIG. 7. FIG. 8, portion (A)represents the energization data generated based on the first printdata, and FIG. 8, portion (B) represents energization data generatedbased on the second print data. In the example illustrated in FIG. 8,portion (B), energization data when the image corresponding to thesecond print data is rotated by 0° (that is, not rotated) isillustrated. The energization data illustrated in FIG. 8, portion (A)includes a value “1” in columns for “A” and “B” for the front portionand the rear portion rows, and a value “0” in columns for “C” to “F” forthe front portion and the rear portion rows. The energization dataillustrated in FIG. 8, portion (B) includes a value “1” in column for“E” and “F” for the front portion and the rear portion rows, and a value“0” in columns for “A” to “D” for the front portion and the rear portionrows.

However, the energization data if the second print data is rotated by180° corresponds to FIG. 9. FIG. 9 is thus a diagram illustrating anexample of the energization data for each print data item depicted inthe example of FIG. 7. The energization data illustrated in FIG. 9includes a value “1” in columns for “A” and “B” in the front portion andthe rear portion rows, and a value “0” in columns for “C” to “F” in thefront portion and the rear portion rows. That is, after rotation of thedata depicted in FIG. 8, portion (B), the result corresponds to FIG. 9.

FIG. 10 is a diagram illustrating temporal transitions of thetemperature of the fixing device 50 and the supplied power when thesecond print data is not rotated (corresponding to rotation by 0°). FIG.10, portion (A) is a diagram illustrating a temporal transition oftemperature when power is supplied to the heater elements 53-1 and 53-2that heat the ranges of “A” and “B” in the fixing device 50. FIG. 10,portion (B) is a diagram illustrating a temporal transition oftemperature when power is supplied to the heater elements 53-5 and 53-6that heat the ranges of “E” and “F” in the fixing device 50. FIG. 10,portion (C) is a diagram illustrating a temporal transition of powerwhen power is supplied to the heater elements 53-1 and 53-2 that heatthe ranges of “A” and “B” in the fixing device 50. FIG. 10, portion (D)is a diagram illustrating a temporal transition of power when power issupplied to the heater elements 53-5 and 53-6 that heat the ranges of“E” and “F” in the fixing device 50.

In the example illustrated in FIG. 10, portion (A), when the first printdata is printed, power is supplied to the heater elements 53-1 and 53-2that heat the ranges of “A” and “B”. When the second print data isprinted, power is supplied to the heater elements 53-5 and 53-6 thatheat the ranges of “E” and “F”. When switching between printing thefirst print data and the second print data, energization is started attime t0 for the heater elements 53-5 and 53-6. As a result, power for aregion P0 is expended until time t1 when the sheet for the second printjob (second print data) finally reaches the fixing device 50.

FIG. 11 is a diagram illustrating a temporal transition of thetemperature of the fixing device 50 and the supplied power when thesecond print data is rotated by 180°. FIG. 11, portion (A) is a diagramillustrating a temporal transition of temperature when power is suppliedto the heater elements 53-1 and 53-2 that heat the ranges of “A” and “B”in the fixing device 50. FIG. 11, portion (B) is a diagram illustratinga temporal transition of power when power is supplied to the heaterelements 53-1 and 53-2 that heat the ranges of “A” and “B” in the fixingdevice 50.

In the example illustrated in FIG. 11A, when the first print data andthe second print data are printed, power is supplied to the heaterelements 53-1 and 53-2 to heat the ranges of “A” and “B”. When switchingbetween printing the first print data and the second print data, thereis residual heat left over from printing the first print data.Therefore, when energization of the heater elements 53-1 and 53-2 isstarted at time t2, power for a region P1 is expended until time t3 whenthe sheet reaches the fixing device 50. Therefore, when FIGS. 10 and 11are compared to each other, the power consumption for printing the twodifferent jobs back to back is different, and more particularly regionP1< region P0.

As described above, in a situation such as depicted in FIG. 7, the powerconsumption is less when the arrangement of the second code data isrotated by 180°. When print data is continuously printed, it isconsidered that the power consumption is reduced when the energizationstate of the rear portion of the first print data and the energizationstate of the front portion of the second print data are made to match.

Based on the above, the image processing unit 74 determines whether ornot to rotate the image corresponding to the second code data based onthe energization data of each continuous print data item. Specifically,first, the image processing unit 74 performs a logical operation on theenergization data of the rear portion of the first print data and theenergization data of the front portion when the image corresponding tothe second print data is rotated by 0° (i.e., not rotated). The imageprocessing unit 74 performs a logical operation (for example, AND) onthe energization data of the rear portion of the first print data andthe energization data of the front portion when the image correspondingto the second print data is rotated by 180°.

FIG. 12 is a diagram illustrating the result of a logical operation(“&”) when the image corresponding to the second print data is rotatedby 0°. It is assumed that the energization data of the rear portion inthe first print data and the energization data of the front portion whenthe image corresponding to the second print data is rotated by 0° are inthe state of FIG. 12. At this time, the image processing unit 74performs a logical operation on the energization data between the heaterelements 53 that heat the same range. For example, the image processingunit 74 performs an AND operation on the energization data between theheater elements 53 that heat the same range. As a result, when the imagecorresponding to the second print data is rotated by 0°, the result ofthe logical operation of each heater element 53 that heats the ranges of“A” to “F” becomes 0.

When the result of the AND operation is “1”, it means that there arecorresponding images at the rear portion of the first print data and atthe front portion of the second print data. Therefore, when the resultof the AND operation is “1”, it can be more efficient to continuouslyenergize from the printing of the rear portion of the first print datato the printing of the front portion of the second print data. On theother hand, when the result of the AND operation is “0”, it means thatimages are not continuous from the rear portion of the first print datato the front portion of the second print data. Therefore, when theresult of the AND operation is “0”, it can be more efficient not tocontinuously energize between the printing of the rear portion of thefirst print data to the printing of the front portion of the secondprint data.

FIG. 13 is a diagram illustrating a result of a logical operation whenthe image corresponding to the second print data is rotated by 180°. Itis assumed that the data of the rear portion included in theenergization data of the first print data and the data of the frontportion included in the energization data of the second print data arethe data in FIG. 13. At this time, the image processing unit 74 performsa logical operation (for example, AND) on the energization data betweenthe heater elements that heat the same range. As a result, when theimage corresponding to the second print data is rotated by 180°, theresult of the logical operation on the energization data for “A” and “B”becomes 1. When the image corresponding to the second print data isrotated by 180°, the result of the logical operation on the energizationfor “C” to “F” becomes 0.

Based on the results of FIGS. 12 and 13, it can be seen that the totalnumber of “1” entries is larger after the logical operation if the imagecorresponding to the second print data is rotated by 180°. A largenumber of “1” entries after the logical operation means that the imagesin the different print jobs are continuous. In the examples illustratedin FIGS. 12 and 13, the power consumption can be reduced when the imagecorresponding to the second print data is rotated by 180° as compared towhen the image corresponding to the second print data is rotated by 0°.For this reason, the image processing unit 74 determines that the imagecorresponding to the second print data is to be rotated by 180°.Hereinafter, it is assumed that a rotation condition is satisfied if thepower consumption can be reduced by rotating the second print data by180°.

FIG. 14 is a flowchart illustrating a flow of processing when the imageforming apparatus 1 according to the embodiment prints print data. Theprocessing of FIG. 14 is executed after a print execution instruction isgiven.

The image processing unit 74 reads the code data stored in the auxiliarystorage device 120 (ACT 201). The image processing unit 74 reads theenergization data stored in the auxiliary storage device 120 (ACT 202).The image processing unit 74 determines whether or not the rotationcondition is satisfied based on the energization data (ACT 203). If therotation condition is satisfied (ACT 203: YES), the image processingunit 74 decompresses the second code data while rotating the second codedata (ACT 204).

On the other hand, if the rotation condition is not satisfied (ACT 203:NO), the image processing unit 74 decompresses the second code data (ACT205). That is, if the rotation condition is not satisfied, the imageprocessing unit 74 determines not to rotate the image corresponding tothe second code data. After the processing of ACT 204 or ACT 205, theimage forming unit 30 forms an image on the sheet based on thedecompressed print data (ACT 206). The fixing control circuit 51energizes the target heater element (s) based on the decompressed printdata (ACT 207). Then, the sheet is heated by the target heater element(s) of the heating unit 52, whereby the image is fixed on the sheet (ACT208). Thereafter, the image processing unit 74 determines whether or notthere is other print data (ACT 209). If there is other print data (ACT209: YES), the image processing unit 74 reads the other print data andagain executes the processing after ACT 201.

On the other hand, if there is no other print data (ACT 209: NO), theimage processing unit 74 ends the processing of FIG. 14.

With the image forming apparatus 1 configured as described above, thetime required for printing can be reduced. Specifically, the imageforming apparatus 1 generates energization data of the rear portion inthe first print data and energization data of the front portion in thesecond print data before compressing the print data. The image formingapparatus 1 determines whether or not it is necessary to rotate theimage corresponding to the second print data by using each generatedenergization data item. Then, the image forming apparatus 1 controls therotation of the second print data according to the determination result.As a result, when the rotation of the second print data is necessary,the image forming apparatus 1 decompresses the second code data whilerotating the second code data. On the other hand, when the rotation ofthe second print data is not necessary, the image forming apparatus 1decompresses the second code data without rotating the second code data.Therefore, it is not necessary to determine whether or not rotation isnecessary after all the print data is decompressed at the time ofprinting. For this reason, it is possible to reduce the time requiredfor printing.

When printing a plurality of pieces of print data continuously, theimage forming apparatus 1 performs a logical operation on theenergization data of the rear portion in the first print data and theenergization data of the front portion in the second print data. At thistime, the image forming apparatus 1 uses the energization data of thefront portion when the image corresponding to the second print data isrotated and the energization data of the front portion when the imagecorresponding to the second print data is not rotated. Specifically,first, the image forming apparatus 1 performs a logical operation on theenergization data of the rear portion in the first print data and theenergization data of the front portion when the image corresponding tothe second print data is not rotated. Further, the image formingapparatus 1 performs a logical operation on the energization data of therear portion in the first print data and the energization data of thefront portion when the image corresponding to the second print data isrotated. Then, the image forming apparatus 1 determines whether or notrotation is necessary based on the result of the logical operation (forexample, AND operation) on each energization data item. For example, theimage forming apparatus 1 determines whether or not rotation isnecessary based on the number of logical operation results of eachenergization data item indicating 1. A large number of 1 as a result ofthe logical operation means that the images are continuous. Therefore,the image forming apparatus 1 determines whether or not rotation isnecessary because the power consumption can be reduced if the number oflogical operation results of each energization data item indicating 1 islarger. Then, the image forming apparatus 1 determines the rotation ofthe second print data based on the determination result. Therefore,power consumption can be reduced.

Hereinafter, a modification example of the image forming apparatus 1will be described.

The image processing unit 74 may generate energization data of the rearportion in the sub-scanning direction of the first print data andenergization data of the front portion in the sub-scanning direction ofthe second print data. That is, the image processing unit 74 may notgenerate the energization data of the front portion in the sub-scanningdirection of the first print data. Further, the image processing unit 74may not generate the energization data of the rear portion in thesub-scanning direction of the second print data.

As described above, if there is energization data of the rear portion inthe first print data and energization data of the front portion in thesecond print data, the necessity of rotation of the second print datacan be determined. With this configuration, the amount of calculationperformed by the image processing unit 74 can be reduced.

When continuously printing print jobs, the image forming apparatus 1 mayin some instances change the printing order of the jobs in considerationof energization data of each print data item. Here, three pieces ofprint data (first print data, second print data, and third print data)will be described as an example. Specifically, the image processing unit74 generates energization data of the front portion and the rear portionin each print data item in conjunction with the generation of the codedata of each print data item. The image processing unit 74 performs alogical operation on each combination pattern of the energization dataof each print data item when a print execution instruction is given. Atthis time, the image processing unit 74 also uses energization data whenthe image corresponding to the print data is rotated. The imageprocessing unit 74 determines the combination having a larger number oflogical operation results indicating “1” as the printing order of printdata. For example, it is assumed that the printing order of the firstprint data, the third print data, and the second print data is acombination providing a large number of logical operation resultsindicating “1”. In this case, the image processing unit 74 selects thiscombination as the printing order. The image processing unit 74 causesthe printing to be executed in the selected order.

With this configuration, the image processing unit 74 can efficientlyexecute printing by changing the printing order of print jobs or thelike. Specifically, the image processing unit 74 changes the printingorder so that the switching of energization to the heater elements 53 isreduced or minimized. Then, the image processing unit 74 changes theprinting order so that printing is performed in the selected order.Therefore, power consumption can be reduced.

With the image forming apparatus 1 according to at least one embodimentdescribed above, the heating unit 52 and the image processing unit 74are provided. The heating unit 52 includes heater elements 53-1 to 53-N.The image processing unit 74 generates first energization data relatedto the first print data and second energization data related to thesecond print data before compressing the first print data and the secondprint data. The image processing unit 74 determines whether or not torotate the second print data for printing based on the generated firstenergization data and second energization data. Then, the imageprocessing unit 74 controls the rotation of the second print dataaccording to the determination result to execute the printing. Thus, itis not necessary to determine whether or not rotation is necessary afterall print data is decompressed at the time of printing. For this reason,it is possible to reduce the time required for printing.

Some functions of the image forming apparatus 1 in the above-describedembodiment may be realized by a general-purpose computer. In that case,a program for realizing these functions is recorded on a non-transitorycomputer-readable recording medium. The described functions may berealized by causing a computer or a computer system to read and executethe program recorded on a recording medium. The “computer system”referred to here includes an operating system and hardware such asperipheral equipment/devices. In addition, “computer-readable recordingmedium” refers to a portable medium, a storage device, or the like. Theportable medium can be a flexible disk, a magneto-optical disk, a ROM, aCD-ROM, or the like. In addition, the storage device can be a hard diskbuilt in the computer system or the like. Furthermore, the“computer-readable recording medium” can be cloud-based and/ordownloadable (or otherwise accessible) via a network connection such asa communication line or cable. The communication line can be a networksuch as the Internet, a telephone line, or the like. The“computer-readable recording medium” may be a network server or a clientterminal, whether virtualized or tangible, accessible across a networkor otherwise. Further, the above-described program may be realizevarious functions in conjunction with another program, an operatingsystem, or the like.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

1. An image forming apparatus, comprising: an image forming deviceconfigured to form images on sheets; a heater including a plurality ofheater elements arranged in a first direction and configured to fiximages to the sheets from the image forming device; and a controlcircuit configured to: divide an image region of first raster image datarepresenting a first image to be formed by the image forming device intoa plurality of first sub-regions; perform a first noise reduction on thefirst image by determining, with respect to each of the firstsub-regions, whether or not a number of color pixels is greater than athreshold; generate first energization data indicating energizationstates of each of the heater elements based on a result of the firstnoise reduction, compress the first raster image data into firstcompressed image data, and store the generated first energization dataand the first compressed image data in a storage; divide an image regionof second raster image data representing a second image to be formed bythe image forming device after the first image into a plurality ofsecond sub-regions; perform a second noise reduction on the second imageby determining, with respect to each of the second sub-regions, whetheror not a number of color pixels is greater than the threshold; generatesecond energization data indicating energization states of each of theheater elements based on a result of the second noise reduction,compress the second raster image data into second compressed image data,and store the generated second energization data and the secondcompressed image data in the storage; and determine whether rotation ofthe second image by a predetermined degree will lower power consumptionbased on a comparison of the first energization data to the secondenergization data.
 2. The image forming apparatus according to claim 1,wherein the control circuit is further configured to: convert the secondcompressed image data to third compressed image data representing athird image obtained by rotating the second image by the predetermineddegree; and decompress the third compressed image data into third rasterimage data.
 3. The image forming apparatus according to claim 2, whereinthe control circuit is further configured to: decompress the secondcompressed image data into the second raster image data; and control theimage forming device to form the second image based on the second rasterimage data.
 4. The image forming apparatus according to claim 1, whereinthe control circuit is configured to: generate the first energizationdata based on a portion of the first raster image data representing apart of the first image including a trailing end in a sub-scanningdirection; and generate the second energization data based on a portionof the second raster image data representing a part of the second imageincluding a leading end in the sub-scanning direction.
 5. The imageforming apparatus according to claim 1, wherein the predetermined degreeis 180°.
 6. The image forming apparatus according to claim 1, whereineach binary bit of the first energization data indicates an energizationstate for a corresponding one of the heater elements, each binary bit ofthe second energization data indicates an energization state for acorresponding one of the heater elements, and the control circuitperforms a logical operation on the first energization data and thesecond energization data to determine whether rotation of the secondimage by the predetermined degree will lower power consumption.
 7. Theimage forming apparatus according to claim 6, wherein the logicaloperation is an AND operation.
 8. The image forming apparatus accordingto claim 1, wherein the image forming device form images on sheets witha toner. 9-13. (canceled)
 14. An image forming method, comprising:dividing an image region of first raster image data representing a firstimage to be formed by an image forming device into a plurality of firstsub-regions; performing a first noise reduction on the first image bydetermining, with respect to each of the first sub-regions, whether ornot a number of color pixels is greater than a threshold; generatingfirst energization data indicating required energization states of eachof a plurality of heater elements in a fixing device based on a resultof the first noise reduction, compressing the first raster image datainto first compressed image data, and storing the generated firstenergization data and the first compressed image data in a storage;dividing an image region of second raster image data representing asecond image to be formed by the image forming device after the firstimage into a plurality of second sub-regions; performing a second noisereduction on the second image by determining, with respect to each ofthe second sub-regions, whether or not a number of color pixels isgreater than the threshold; generating second energization dataindicating required energization states of each of the plurality ofheater elements based on a result of the second noise reduction,compressing the second raster image data into second compressed imagedata, and storing the generated second energization data and the secondcompressed image data in the storage; and determining whether rotationof the second image by a predetermined degree will lower powerconsumption based on a comparison of the first energization data to thesecond energization data.
 15. The image forming method according toclaim 14, wherein the predetermined degree is 180°.
 16. The imageforming method according to claim 14, further comprising: generatingthird image data using the second compressed image data when it isdetermined that rotation of the second image by the predetermined degreewill lower power consumption; and forming a third image, instead of thesecond image, on a sheet with the image forming device when it isdetermined that rotation of the second image by the predetermined degreewill lower power consumption based, third image being formed based onthe third image data.
 17. The image forming method according to claim16, wherein the predetermined degree is 180°.
 18. The image formingmethod according to claim 14, wherein the image forming device formsimages on sheets with a toner.
 19. The image forming method according toclaim 14, wherein the image forming device forms images on sheets with aplurality of toners.